1. Field of the Invention
The present invention relates to a laser beam irradiation apparatus configured to irradiate a laser beam on a work and a laser working machine which includes the laser beam irradiation apparatus.
2. Description of the Related Art
In a semiconductor device fabrication process, a plurality of regions are defined by division plan lines called streets arranged in a grid-like fashion on the surface of a semiconductor wafer having a substantial disk shape, and devices such as an IC, an LSI, and so forth are formed on the sectioned regions. Then, the semiconductor wafer is cut along the division plan lines so that the regions in which the devices are formed are divided to fabricate individual semiconductor chips. In order to implement downsizing and higher functionalization of an apparatus, a module structure in which a plurality of semiconductor chips are laminated and electrodes of the laminated semiconductor chips are connected to each other has been placed into practical use. As disclosed, for example, in Japanese Patent Laid-open No. 2003-163323, the module structure is configured such that a through-hole (via hole) is formed at a portion of a semiconductor wafer at which an electrode is formed and a conductive material to be connected to the electrode such as aluminum is filled in the through-hole (via hole).
The through-hole (via hole) provided in the semiconductor wafer described above is formed by means of a drill. However, since the diameter of the through-hole (via hole) provided in the semiconductor wafer is as small as 100 to 300 μm, there is a problem that, where a drill is used to form a hole, the productivity is low. In order to eliminate the problem described above, the assignee of the present application has proposed a laser working apparatus which can effectively form a fine hole in a work such as a semiconductor wafer or the like in Japanese Patent Application No. 2005-64867. The laser working apparatus includes working feeding amount detection means configured to detect a relative working feeding amount between a chuck table for holding a work and laser beam irradiation means, and storage means configured to store X and Y coordinate values of a pore formed on the work. The laser working apparatus further includes control means configured to control the laser beam irradiation means based on the X and Y coordinate values of the fine hole stored in the storage means and a detection signal from the working feeding amount detection means. The laser working apparatus is configured such that a one-pulse laser beam is irradiated if the X and Y coordinate values of the fine hole formed in the work indicate a position just below a condenser of the laser beam irradiation means.
However, while it is necessary, in order to form a fine hole in a work, for a pulse laser beam to be irradiated on the same portion by a plural number of times, where the laser working apparatus described above is used, the movement of the work must be performed by a plural number of times. Therefore, the laser working apparatus is not necessarily satisfactory from a point of view of the productivity. Further, it is preferable to form a plurality of laser working grooves on a work only if working feeding is performed without performing indexing feeding of the work in an indexing feeding direction (Y-axis direction) orthogonal to a working feeding direction (X-axis direction).
In order to satisfy such a demand as just described, the assignee of the present application has proposed a laser working apparatus in Japanese Patent Application No. 2005-362236. The laser working apparatus includes laser beam irradiation means having acousto-optic deflection means in which an acousto-optic device is used, and deflects a laser beam oscillated by laser beam oscillation means when it passes the acousto-optic device so that the laser beam is irradiated at the same working position while performing working feeding of a work.
However, the acousto-optic deflection means is formed from an acousto-optic device for deflecting a laser beam oscillated from the laser beam oscillation means, a RF oscillator for applying a RF (radio frequency) to the acousto-optic device, a deflection angle adjustment means for adjusting the frequency of the RF to be outputted from the RF oscillator and an output adjustment means for adjusting the amplitude of the RF to be generated by the RF oscillator. Therefore, there is a problem that, if the RF is continuously applied to the acousto-optic device, then since thermal distortion appears on the acousto-optic device, an error occurs with the deflection angle of the laser beam and an output of the laser beam becomes non-uniform, resulting in failure in high accuracy working.